1. Field of the Invention
The present invention relates to a process for preparing air-entrained concrete or air-entrained mortar by using a non-air-entraining type high-range water-reducing agent for concrete, a foaming compound and a foam stabilizer in combination. In the description, the wording "air-entrained" is abbreviated as "AE".
2. Description of the Prior Art
Attainment of such effects as (1) improvement of the workability and resulting reduction of the water-cement ratio and the quantity of fine aggregate, (2) increase of the water-retaining force by air bubbles and resulting reduction of bleeding, (3) improvement of the pumpability and (4) improvement of the resistance to freezing and thawing can be expected by incorporating an additive for imparting the air-entraining property (hereinafter referred to as "AE agent") into concrete or mortar.
As popular AE agents, there can be mentioned anionic surface active agents comprising as main ingredients highly oxidized resin acid salts, salts of protein substances, salts of alkyl benzene-sulfonates, triethanolamine salts of alkyl sulfonates and polyoxyethylene alkyl sulfonates, and non-ionic surface active agents comprising polyoxyethylene alkyl aryl ethers, etc.
As the air-entraining type water-reducing agent (hereinafter referred to as "AE water-reducing agent"), there can be mentioned sulfonic acid salts of aromatic hydrocarbon-formalin condensates represented by salts of lignin sulfonate, salts of alkyl naphthalene sulfonate-formalin condensates and sulfonic acid salts of creosote oil decomposition product hydrocarbon-formalin condensates.
As typical instances of the high-range water-reducing agent for concrete, there can be mentioned a high condensate of a .beta.-naphthalene-sulfonic acid-formaldehyde condensate (see Japanese Pat. No. 11737/66) and a sulfonic acid salt of a melamine-formaldehyde polymer (Japanese patent application Laid-Open Specification No. 8080/72), and each of them is of the non-air-entraining type.
Non-air-entraining type high-range water-reducing agents have heretofore been used mainly for so-called high-strength concrete. On the other hand, AE agents or AE water-reducing agents have heretofore been used mainly for construction concrete or concrete having a relatively low strength. Accordingly, a non-air-entraining type high-range water-reducing agent and an AE agent have hardly been used in combination.
Recently, in Germany, a sulfonic acid salt of a melamine-formalin polymer, i.e., a high-range water-reducing agent, has been used as a fluidizing agent for fluidized concrete (Fliss Beton). Furthermore, it has been found that a salt of a high molecular weight condensate of .beta.-naphthalene-sulfonic acid with formalin has very excellent properties as a fluidizing agent for fluidized concrete.
However, it has been experienced that in the preparation of fluidized concrete, bubbles of air entrained into base concrete (concrete before incorporation of a fluidizing agent) with use of an AE agent or AE water-reducing agent are caused to disappear by addition of the above-mentioned fluidizing agent of the high-range water-reducing agent type and attainment of the effects expected for AE concrete, especially the effect of improving the resistance to freezing and thawing, can hardly be attained. Furthermore, in the manufacture of high-strength prestressed concrete products which are exposed to the outer air and undergo freezing and thawing, for example, railroad ties, track slabs and bridge girders, a high-range water-reducing agent and an AE agent are often used in combination. Also in this case, bubbles of entrained air are caused to disappear. In other words, if only a commercially available high-range water-reducing agent and a commercially available AE agent are combined, it is impossible to obtain concrete which is satisfactory in both the high fluidizing property in fresh concrete and the air-entraining property in hardened concrete. American Concrete Institute (ACI) proposed that in connection with the resistance to freezing and thawing, an important characteristic of AE concrete, the air void spacing factor should be less than 250 .mu., preferably less than 200 .mu., and this air void spacing factor is regarded as an important factor in the manufacture of AE concrete as well as the durability factor at the freezing-thawing test.
When a commercially available AE agent or AE water-reducing agent is used singly, the air void spacing factor of the resulting concrete is less than 200 .mu. or slightly larger than 200 .mu., and the resistance to freezing and thawing is sufficient. However, when such AE agent or AE water-reducing agent is used in combination with a high-range water-reducing agent (fluidizing agent), even if it is used in an amount larger than the customarily used amount, the air void spacing factor becomes larger than 250 .mu. and the resistance to freezing and thawing is reduced.